Systems for selecting needles using electromagnets as selection actuators have already been proposed in the field of stocking knitting machines. These electromagnets cooperate, by means of mechanical elements, with the deflected lower needles in order to control their passage from a deflected, inoperative position to a released, operating position, in which they can control the corresponding needles.
A circular knitting machine is disclosed in U.S. Pat. No. 5,165,259 to Negri et al. In this device the inactivation or activation of a vertical jack below each needle is determined by a flexible fork located radially above the cylinder within a ring structure completely surrounding the machine cylinder and rigid therewith. A number of forks and radial grooves equal to the number of needles is provided. The forks are able to flex within the grooves and are selected by magnetic force. The jacks are kept in position by one or more circular springs surrounding the upper part of the jacks. The springs must be sufficiently shrunk to oppose the forces which flex the jack shank, so that the flexing forces acting on the foot effect the flexture without causing the upper end of the jack to leave the trick.